Influence of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu2O3:2%Yb, 0.2%Tm nanopowders

Lutetium oxide nanopowders codoped with Tm³⁺ and Yb³⁺ were synthesized by the reverse-strike co-precipitation method. Effects of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu₂O₃:2%Yb, 0.2%Tm nanopowders had been investigated. The results show that pH value of the precipitant (NH₄HCO₃) solution has a significant effect on the particle size, morphology and upconversion emission intensity of the Lu₂O₃:2%Yb, 0.2%Tm nanopowders. All the samples obtained from different pH value of precipitant solution can be readily indexed to pure cubic phase of Lu₂O₃, indicating good crystallinity. The upconversion emission intensity of Lu₂O₃:2%Yb, 0.2%Tm nanopowders obtained from the precipitant solution with pH=11 is the strongest. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing the number of OH⁻ groups and the enlarged nanopowder size. The strong blue, weak red and near infrared emissions from the prepared nanopowders were observed under 980 nm laser excitation, and attributed to the ¹G₄→³H₆, ¹G₄→³F₄ and ³H₄→³H₆ transitions of Tm³⁺ ion, respectively.     

Novel red perovskite phosphor Ca2AlNbO6:Eu for white light-emitting diode application

Eu³⁺-doped perovskite phosphors of Ca₂AlNbO₆ were synthesized from a solid state reaction. A small amount of the Li₂CO₃ flux was found to greatly shorten calcination time and reduce reaction temperature. The structural and optical properties of the samples were systematically investigated. The excitation spectra of Ca₂AlNbO₆:Eu³⁺ reveal two excitation bands at 398 (⁷F₀→⁵L₆) and 466 nm (⁷F₀→⁵D₂), which match well with the two popular emissions from near-UV and blue LED chips. Under blue light excitation, the red emission of Ca₂AlNbO₆:0.05Eu³⁺ is twice more intense than that of (Y_0.95Eu_0.05)₂O₃. The chromaticity coordinates of (Ca_0.95Eu_0.05)₂AlNbO₆ (x=0.654, y=0.346) are close to the standard values (x=0.670, y=0.330) of National Television Standard Committee (NTSC). The optical properties suggest that Ca₂AlNbO₆:Eu³⁺ is an efficient red-emitting phosphor for light-emitting diode applications.     

Phase-matched high-order harmonics by interaction of Ar atoms with high-repetition-rate low-energy femtosecond laser pulses

High-order harmonics are generated by coherent interaction of an intense laser and atoms or molecules[1]. With the development of the intense ultrashort pulse laser, the research of high-order harmonic generation has reached the water-window in spectral region[2] and subfemtosecond in time domain[3]. Especially, the generation and application of subfemtosecond pulse led the study of high-order harmonic generation into a completely new world[4, 5]. It has made the study of ultrafast science fro…     

Electroless deposition of open-end Cu nanotube arrays

Cu nanotube arrays were fabricated by electroless deposition using porous anodic aluminium oxide membranes as templates. This was accomplished by a four-step procedure, i.e. pore-wall modification, polishing treatment, sensitization-activation and electroless deposition. The as-synthesized Cu nanotubes possess controllable inner diameter and open ends.     

Spectroscopic properties of Yb3+-doped Y3Al5O12 nano-ceramics obtained under different sintering pressures

Yb³⁺:YAG nano-ceramics have been obtained by a low temperature/high pressure sintering process. Structural properties have been studied by X-ray diffraction (XRD). Grain sizes and R.M.S micro-strains have been calculated based on the XRD patterns by Rietveld analysis method. Emission spectra and decay curves have been recorded and analyzed. It has been observed that the decay time decreases with the increase of sintering pressure. Presence of Yb³⁺–Yb³⁺ pairs have been detected by cooperative emission spectroscopy.     

One color contrast enhanced infrared and visible image fusion method

Color constancy (Toet and Franken, 2003 [2]; Toet, 2003 [7]) and color contrast (Scribner et al., 2000 [21]; Lee et al., 2005 [23]) are two important topics for color image fusion. The paper focuses on the low color contrast problem of linear fusion algorithms with color transfer method. Color transfer technology is popular in infrared (IR) and visible image fusion to give the fused image a natural day-time color appearance (Toet, 2003 [7]; Wang et al., 2007 [8]; Zheng and Essock, 2008 [9]). However, in the color transfer step, all three channels of the color space are processed with the same linear mapping without color enhancement, resulting in low color contrast between the target and the background (Wang et al., 2007 [8]). Based on the characteristics of the IR image, we introduce a ratio of local to global divergence of the IR image to improve the color contrast. The enhancement ratios for both hot and cold targets are larger than one, while it tends to one for the background. As a result, the proposed method pops out both hot and cold targets in color, where hot targets will appear intense red, and cold targets will appear cyan. Subjective results show visible color contrast enhancement effects. Target detection experiments through hue and saturation components of the fused image show an improvement in the hit rate for target detection, owing to larger color distance between the target and the background.     

分辨率对大气中痕量污染气体的DOAS测量性能影响研究

在差分吸收光谱(DOAS)测量过程中,光谱分辨率的选择直接决定了污染气体浓度的测量准确度.主要研究了光谱分辨率对污染气体被榆测到的特征吸收结构形状的影响,以及差分吸收截面随分辨率的变化趋势,从而确定了光谱分辨率对污染气体最低可检测浓度的影响,通过研究分辨率与光强的关系,确定了分辨率与信噪比(S/N)的函数关系式,得出了DOAS测量NO2,O3,和SO2的最佳信噪比范围,对多种污染物标准气体进行了同时监测,计算出标准气体在不同光谱分辨率下的测量误差,确定了对NO2,O3和SO2监测的最适用的分辨率范围.在此分辨率范围既能够实现对痕量气体的准确定性定量测量,又能达到测量所需要的高灵敏度,强选择性和适用的时间分辨率.通过在北京丰台区的实际监测得到了与点式仪器测量结果很好的一致性.     

芦丁对血清白蛋白构象的影响

用同步荧光光谱法和圆二色谱法研究了芦丁对牛血清白蛋白(BSA)和人血清白蛋白(HSA)构象和功能的影响,同时用电化学方法研究了芦丁与血清白蛋白之间的结合作用。在体内随着芦丁浓度的增加,其与血清白蛋白结合时对血清白蛋白的构象无影响,但对血清白蛋白的二级结构有影响,导致α-螺旋结构减少,β-折叠结构增加,蛋白质的二级结构被破坏。电化学研究发现：芦丁的氧化还原电流随着血清白蛋白浓度的增加而明显降低, 表明芦丁与血清白蛋白发生反应,生成比较稳定的复合物。芦丁的氧化还原最大峰电位也随着血清白蛋白浓度的增加发生变化,峰电位差略增加,表明芦丁的氧化还原性随着血清白蛋白浓度的增加而增强。进一步证明芦丁在体内能够被血清白蛋白存储和转运。     

Statistical properties of thermal radiation in a Kerr nonlinear blackbody

We study the statistical properties of thermal radiation in a Kerr nonlinear blackbody in which bare photons with opposite wave vectors and helities are bound into pairs and unpaired photons are transformed into a different kind of quasiparticle, the nonpolariton. This paper investigates the statistical properties of the photon blackbody field by using the second-order correlation function, the phase space distribution function, the photon number distribution and the nonclassical depth. The numerical computation and a discussion of the results are present.     

具有不同取代基团的香豆素系列分子二阶非线性光学性质的DFT研究

本文设计了具有不同取代基团的7-苯乙烯基香豆素和4-苯乙烯基香豆素的A、B两个系列共14个化合物分子.采用密度泛函理论B3LYP/6-31G方法对其几何构型进行了全结构优化.在所得优化结构的基础上对这些分子的稳态二阶非线性光学(NLO)系数β值进行计算分析,同时用含时密度泛函理论(TD-DFT)对这些分子的电子性质进行了研究.结果表明:此类香豆素化合物具有较大的分子β值,其中A类分子的共面性好,共轭链长,β值均比B类分子的大.14个化合物中前线分子轨道能级差越小的化合物,其βwt值越大.各分子前线分子轨道跃迁对二阶NLO效应有明显的贡献.